1. Field of the Invention
The present invention relates to an image forming method, an image forming apparatus, and an ink jet recording apparatus.
2. Description of the Related Art
An ink containing a pigment (pigment ink) as a coloring material providing recorded matter having high image density and excellent in durability and the like has conventionally been used as an ink for writing materials (a fountain pen, a felt pen, a water-based ballpoint pen, etc.) or an ink for use in a ink jet recording method. As the pigment ink, there have been proposed, for example, a black ink containing carbon black and a dispersant and a black ink containing a self dispersion carbon black enabling the pigment to be dispersed without employing a dispersant (see Japanese Patent Application Laid-Open Nos. S63-152681, S64-006074 and H08-003498).
Full-color recorded matter has been commonly used in recent years for various reporting documents and notice materials in offices, schools, stores, and the like. Thus, there is a need to form not only a black image but also a high-quality full-color image. In forming a full-color image, a wide variety of plain papers are used as recording media, such as copying paper, writing paper, notebooks, letter paper, bond paper, and continuous form paper. In addition, a plain paper containing a recycled material has come to be widely used as a recording medium in view of recent demands for environmental protection and resource conservation. Thus, the ink is studied from various aspects such as its composition and physical properties in order to form a high-quality image even when a wide range of plain papers are used as recording media.
An ink jet recording method uses a pigment ink as described above, as a black ink, and forms a full-color image by combination with other color inks. Specific examples of the color ink include at least one selected from magenta ink, cyan ink, yellow ink, red ink, green ink, and blue ink. Here, in a typical ink set, the characteristics of each ink are sometimes controlled as described below. Specifically, the permeability of the color inks into recording media is relatively increased for improved fixability of the inks and reduced occurrence of bleeding between the color inks. In addition, the permeability of the black ink into recording media is set to a relatively lower level than that of the color inks for improved character quality. The formation of an image with an ink set having the foregoing black and color inks may pose problems as described below. Specifically, there may occur a phenomenon in which bleeding appears at the boundary portion between images formed with the black and color inks and a phenomenon in which the image quality is lowered by non-uniform mixing of the black and color inks. For reduction of the occurrence of the bleeding, there has been proposed a recording method involving using a first ink and a second ink capable of reacting with the first ink to supply the second ink to a region to which the first ink is applied to overlap (see Japanese Patent Application Laid-Open No. H11-343441).
When a color ink and a black ink containing a pigment are applied so as to overlap with each other for reduction of the occurrence of the bleeding, the density and color tone of the resultant image vary (that is, color unevenness may occur) depending on the order of applying the color and black inks. For suppression of the color unevenness, there have been proposed an ink set and an image recording method in which the black ink contains a pigment and a salt and the color inks contain a component unstabilizing the dispersion state of the pigment in the black ink (see Japanese Patent Application Laid-Open Nos. 2001-150793 and 2001-152059).
In recent years, in ink jet recording, a method has been carried out which involves causing a recording head to conduct bi-directional scanning twice or more in the main scanning direction to record an image having the same width as the length of the head (herein after referred to as multi-pass recording) in order to make image quality more excellent. However, the multi-pass recording sometimes does not enable sufficient reduction of recording time even when the number of nozzles is increased or even when the length of the recording head is increased. Accordingly, to reduce the recording time, there are attempted a method involving recording an image in each of the forward and return directions of the main scanning (hereinafter referred to as bi-directional recording) and a method involving recording, by one main scanning, an image having the same width as the length of a recording head (hereinafter referred to as single-pass recording). Recording with a combination of single-pass and bi-directional recordings, i.e., single-pass bi-directional recording, eliminates the need to conduct scanning to an identical position on a recording medium plural times, which can greatly reduce the recording time. However, as a result of studies of the present inventors, it has been found that high-speed recording such as the single-pass bi-directional recording poses the following problems. Specifically, such a problem as to generate bleeding markedly has been found out. In addition, such a further problem as to generate color unevenness prominently has been found out when a black ink and a color ink capable of reacting with the black ink are applied so as to overlap with each other as in the invention disclosed in Japanese Patent Application Laid-Open Nos. 2001-150793 and 2001-152059 to reduce the occurrence of bleeding. The single-pass bi-directional recording renders the color unevenness prominent particularly in an image in which an image region recorded by overlaying a black ink with a color ink and an image region recorded by overlaying a color ink with a black ink coexist. In other words, the inventions described in the above Japanese Patent Application Laid-Open Nos. 2001-150793 and 2001-152059 are inadequate as methods for forming, at high speed, a high-level high-quality image as required in recent years even when a wide variety of plain papers are used as recording media.
Thus, an object of the present invention is to provide an image forming method, an image forming apparatus and an ink jet recording apparatus which can suppress the occurrence of bleeding and color unevenness even when bi-directional recording is performed and can provide high image quality.